Plumbagin Triggers ER Stress-Mediated Apoptosis in Prostate Cancer Cells via Induction of ROS.

BACKGROUND/AIMS: Prostate cancer (PCa) is the second most frequently diagnosed cancer in men worldwide. Currently available therapies for hormone-refractory PCa are only marginally effective. Plumbagin (PLB), a natural naphthoquinone isolated from the traditional folk medicine Plumbago zeylanica, is known to selectively kill tumor cells. Nevertheless, antitumor mechanisms initiated by PLB in cancer cells have not been fully defined.

METHODS: MTT assay was used to evaluate the effect of PLB on the viability of cancer cells. Cell apoptosis and reactive oxygen species (ROS) production were determined by flow cytometry. Protein expression was detected by western blotting. In vivo anti-tumor effect was measured by using tumor xenoqraft model in nude mice.

RESULTS: In the present study, we found that PLB decreases cancer cell growth and induces apoptosis in DU145 and PC-3 cells. In addition, by increasing intracellular ROS levels, PLB induced a lethal endoplasmic reticulum stress response in PCa cells. Importantly, blockage of ROS production significantly reversed PLB-induced ER stress activation and cell apoptosis. In vivo, we found that PLB inhibits the growth of PCa xenografts without exhibiting toxicity Treatment of mice bearing human PCa xenografts with PLB was also associated with induction of ER stress activation.

CONCLUSION: Inducing ER stress by PLB thus discloses a previously unrecognized mechanism underlying the biological activity of PLB and provides an in-depth insight into the action of PLB in the treatment of hormone-refractory PCa.